Known artificial turfs are produced either from monofilaments or from flat, narrow fibrillated strips.
Flat fibrillated strips may be fabricated in the following manner, for example. Typically, a film ca. 2 m wide is produced by extrusion, and is then slit into strips of width ca. 20 mm, using a cutter bar. Then the strips are re-heated and are stretched linearly.
The stretched strips are then cut by means of a “fibrillator”. In the “fibrillation” the strip is cut with longitudinal cuts of limited lengths (“sectionwise”), such that a honeycomb pattern is formed in the width of the fibrillated strip, by the individual steps, when the strip is stretched.
Following the “fibrillation”, the strip is re-heated and is shrunk by 10-30% (“relaxation” process). A fibrillated strip has width 6-12 mm and thickness 0.1-0.14 mm. It has a flat, rectangular shape if not subjected to tensile force in the lateral direction. At the end of the apparatus the fibrillated strip is wound onto a spool. One fibrillated strip is always wound onto a single spool.
Such a spool is used in the next production step, in which the fibrillated strip is tufted in a tufting process, to produce an expanse of artificial turf (carpet comprised of artificial turf). For this, the fibrillated strips must be guided by the needles of a tufting machine. In this connection, the eye of the tufting needle is employed for guiding, which eye typically has a diameter of 5-6 mm.
Since the flat, fibrillated strips may have a width up 12 mm, they tend to become caught in the eye of the needle.
To avoid this, typically the strips are subjected to twisting. In the twisting process, the strips are twisted in ca. 30 twists per meter, whereby the shape of the flat strip is brought into a round shape which facilitates passing the strip through the eye of the needle.
The twisting imposes additional stress on the strip, to some extent negatively influencing mechanical performance parameters such as strength and elongation.
In addition, the additional production step of twisting entails substantially higher production costs.
Alternatively, it has been proposed to provide a winding (wrap) around the flat, fibrillated strip, with “folding up” of the fibrillated strip. It has been found that the “folding up” is too non-uniform, and that to an appreciable extent the strip still becomes caught in the eye of the needle.
Accordingly, it is an object of the present invention to devise an economical means of more uniformly and more extensively deforming the flat, fibrillated strip wherewith the strip has the desired mechanical performance and in addition can be passed through the eye of a tufting needle without becoming caught there.